This invention relates to the field of failure analysis of integrated circuits and semi-conductors. More particularly, a self-aligning tool is provided for cross-sectioning an integrated circuit in a hands-free mode of operation.
When an integrated circuit (IC) fails to operate, or fails to operate as expected, it may be subjected to failure analysis in order to determine the cause of the failure. For example, when a newly designed circuit is first manufactured, it is usually tested to ensure that it operates correctly. If it does not, operational testing of the part may be able to identify a symptom of the fault or the general area in which the fault may lie, but may not be able to determine the exact cause of the failure (e.g., bad soldering, an open or shorted line). Therefore, one goal of failure analysis is to determine the cause of the part's failure by examining one or more areas or suspected points of failure.
Thus, failure analysis often requires locating a specific element (e.g., junction, line) or area of an IC for close examination (e.g., under a powerful microscope). Typically, a cross-section of the IC is taken at the suspected area in order to gain an unobstructed view. Because of the microscopic level of detail involved (e.g., sub-micron units of measure in some cases), however, it is essential that just enough of the IC is removed to expose the desired element, but no more.
If a relatively large portion of the circuit must be removed little precision is required at first--i.e., the part may be sawn or cut roughly in order to remove most of the extraneous material. However, in the latter stages of the cross-sectioning effort great care and precision are required in order to uncover the desired area without introducing any new fractures or other errors. Many failure analysis operations employ an abrasive surface, such as a milling disk (e.g., a circular piece of sandpaper), to grind away the edge of the IC to uncover the suspected fault.
One tool for cross-sectioning an IC with a milling disk is a hand-held tool. A die may be secured to this tool, which is then guided by the operator to grind away the unneeded portion of the IC. The die can be removed from the tool for examination (e.g., to determine if the area of interest has been uncovered yet).
This tool is deficient in several respects. First, it requires continuous human operation and attention regardless of how much of the IC needs to be ground away in order to reach the target area. Also, the angle at which the die is cross-sectioned depends upon the angle at which the operator holds the tool. Because there is no mechanism for ensuring that the same angle is maintained throughout the cross-sectioning, the operator may inadvertently remove too much of the IC. In addition, this tool can only be used with IC dies, not packages. Finally, this tool is relatively expensive to use due to the need for constant human attendance.
Another tool for cross-sectioning an IC by grinding an edge with a milling disk is more automated than the tool described above, but still suffers from significant shortcomings. This tool, which can accommodate dies but not packages, includes a mechanical arm to hold an IC for grinding. The IC must be encased in wax, however, in order to be held by the arm. In addition, the arm must be continually adjusted to ensure that the IC is placed in contact with the abrasive surface. The IC must be removed from the arm to be examined, thus requiring the wax to be removed (e.g., melted) prior to examination, and then re-applied if further grinding is necessary. Repeatedly mounting the IC in wax makes it very easy to misalign the IC in between grinding evolutions, and the effort required to repeatedly prepare the IC for examination and then grinding adds a significant amount of time to a failure analysis operation.
Thus, what is needed is a cross-sectioning tool that can operate without a human operator's continuous participation and which facilitates easy re-alignment of an IC that is being cross-sectioned so as to maintain the same angle of cross-sectioning. Also, the tool should be able to handle ICs of various sizes, including both dies and packages.